Depression is a common mental disorder. According to data from the 2017 National Survey on Drug Use and Health, more than 17 million adults in the United States experienced at least one major depressive episode during the previous year.
Like many other mood disorders, depression can vary in severity. While some people develop mild depression, others are affected by severe symptoms that can last for years.
You may have heard that depression is caused by a lack of certain mood-regulating chemicals in your brain.
While this is true, the full truth is a little more complex. Experts have identified a wide variety of factors that can cause depression, from your genetics to stressful life events, trauma and many others.
Below, we’ve provided more information about how depression develops, as well as the factors that may play a role in the process.
We’ve also talked about the different types of depression and the unique factors that can cause each one.
Finally, we’ve explained what you should do if you’re feeling depressed and want to take action to find help, treat your depression and improve your quality of life.
Although depression is one of the most common, frequently treated mood disorders, experts still aren’t fully aware of what causes it to develop.
This is because unlike many other illnesses, which are caused by a specific pathogen or internal dysfunction, research into depression suggests that it can be caused by a variety of factors.
If you’ve researched about depression, you’ve likely heard that depression is linked to unusually low levels of certain neurotransmitters in your brain, such as serotonin.
Neurotransmitters are chemicals that transmit information between your neurons. Experts have currently identified more than 100 different neurotransmitters, many of which play essential roles in your brain and body’s functioning.
Currently, experts believe that several different neurotransmitters may be related to depression and its symptoms. These include:
Most medications for depression work by increasing levels of these neurotransmitters in order to reduce the severity of your depression symptoms and restore your mood.
Other factors related to your brain function, such as nerve circuit functioning, nerve cell growth and nerve cell connections, also play a role in depression.
Certain factors, such as major changes in your life or stress, can make you more vulnerable to depression. These are often referred to as depression risk factors.
People often become depressed when a combination of different factors all take a toll on their mood and quality of life.
For example, being diagnosed with a medical condition can result in financial hardship, stress, reduced social contact and other sudden life changes. This combination of factors can lead to an increased risk of developing depression.
Below, you can find more information about the most common risk factors for depression:
Depression often develops after one or several sudden changes in your life, especially if these changes lead to stress. Life changes that may trigger depression include:
These events often have a negative effect on your mood. While these effects are short-lived for some people, others may experience a more persistent, severe low mood and depression when changes occur suddenly.
Trauma and abuse, especially when they occur during your childhood, may increase your risk of developing depression as an adult.
A range of traumatic events are associated with depression, as well as mental health conditions such as post-traumatic stress disorder (PTSD). Approximately half of all people with PTSD also suffer from major depressive disorder.
You may have a higher risk of developing depression and other mental health issues if you have experienced any of the following as a child:
Other issues within your childhood household, such as substance abuse, parental separation or mental illness, may also increase your risk of developing mental health issues as an adult.
Chronic stress, a constant form of stress that usually occurs over a long period of time, is linked to a range of negative health issues, including anxiety and depression.
Common sources of chronic stress include relationship issues, financial issues or a demanding or dissatisfying work environment. These problems may develop over time, resulting in stress that worsens without any obvious path towards improvement.
Chronic illnesses and conditions that cause pain, especially when undiagnosed or unmanaged, can affect your mood and lead to depression.
These may include serious illnesses such as heart disease, diabetes or cancer, or illnesses that aren’t life-threatening but cause a significant reduction in your quality of life.
Although there’s no single “depression gene,” research indicates that depression has a genetic component.
This means that if your parents or other family members have a history of depression, you may have an elevated risk of developing depression at some point in your life.
According to Stanford University School of Medicine, if you have a parent or sibling with major depression, your risk of developing depression is approximately two to three times higher than the average person’s.
Your risk is higher if you have a parent or sibling affected by recurrent depression -- a form of depression that occurs more than once -- that started early in their life.
You may have a higher risk of developing depression if you’re lonely and spend little or no time around other people.
Loneliness and depression often occur together. Not only can being lonely increase your risk of developing depression, but depression itself can often cause you to withdraw from your normal social life and spend less time around your close friends and family.
Substance abuse, whether it involves illicit drugs or substances such as alcohol, is often linked to depression.
People often use alcohol and other substances to self-medicate due to stress or after traumatic events. For example, someone with a demanding, stressful job may use alcohol to relax after a long, challenging day at work.
Over time, this may trigger or worsen depression. People who are already at risk of developing depression due to a major life change or other issue may be particularly at risk if they begin to abuse alcohol or other substances.
Certain medications, including numerous widely-used prescription drugs, are associated with an elevated risk of depression.
Medications that may increase your risk of developing depression include certain antiviral drugs, cardiovascular medications, antidepressants, anticonvulsants, hormonal medications, oral acne medications, antipsychotics and smoking cessation agents.
Some other medications, such as opioid painkillers, may also contribute to an heightened risk of developing depression when misused or abused.
Finally, certain personality traits may make you more likely to develop depression or other mood disorders.
Research into the relationship between personality traits and depression has found that people who are depressed tend to display higher levels of neuroticism than the general population.
Neuroticism is defined as a tendency towards feelings such as self-doubt, irritation, anxiety and other negative emotions.
People with depression also typically score lower on personality traits such as extraversion and conscientiousness.
Most people associate the word “depression” with major depression, also referred to as major depressive disorder. This is a classic form of depression that can cause a persistent low, dark mood and other symptoms such as loss of energy, sleep issues and negative feelings.
In addition to major depression, there are several other forms of depression, some of which are caused by specific events or behaviors. These include:
If you’re feeling depressed, it’s important to seek help. Depression is treatable, and talking to a licensed healthcare provider is an excellent first step towards overcoming your depression and working towards recovery.
Depression can be treated through medication, therapy and certain changes to your habits and lifestyle.
Your healthcare provider may prescribe antidepressants to improve your mood and treat your depression. These work by increasing your production of neurotransmitters that regulate your moods and feelings.
Although antidepressants are effective, you may not notice their effects right away. It generally takes four to eight weeks before you’ll notice any improvement in your symptoms.
Often, the cause of your depression will play a role in determining the most effective treatment method for you.
If suitable, your healthcare provider may recommend that you take part in psychotherapy, such as cognitive behavioral therapy (CBT) or interpersonal therapy (IPT).
These forms of therapy can teach you new methods of thinking and behavioral approaches to overcome depression. In certain cases, your healthcare provider may recommend other forms of therapy.
Finally, you may be able to improve your recovery from depression by making certain changes to your habits and lifestyle, such as:
You can learn more about recovering from depression using medication, psychotherapy, lifestyle changes and more in our full guide to fighting depression.
At a basic level, experts believe depression occurs when you have too little of certain chemicals, called neurotransmitters, in your brain.
Current research shows that a variety of factors may contribute to the changes in your brain that cause depression. These include major life changes, traumatic or abusive experiences, genetics and even certain personality traits.
If you feel depressed, you can seek help by talking to a licensed healthcare provider to receive science-based, effective treatment.